1. Field of the Invention
This invention relates generally to programmable power supplies and, more specifically, to a programmable synchronous step down dc--dc converter controller and, even more specifically, to a programmable synchronous step down dc--dc converter controller suitable for use in current and future computer systems in which the CPU in the computer system is programmed to signal the controller what voltage is required and wherein the controller automatically supplies the required voltage.
2. Discussion of the Related Art
In the past ten years, the microprocessor has evolved from an integrated semiconductor chip that could control only simple functions to something that can rival the computing power of a mainframe computer. That evolution has brought ever increasing numbers of transistors being integrated onto a single chip and, as an example, the current Intel Pentium.RTM. microprocessor chip integrates well over 5 million transistors on a single piece of silicon. Other microprocessor chip manufacturers integrate similar numbers of transistors on their chips. In order to achieve this kind of density, the physical geometry of each transistor has had to be reduced to the sub-micron level and with each successive design geometry shrink, the corresponding maximum voltage within which the transistor is to operate has had to be reduced as well. This changing maximum operating voltage for microprocessors has led to the need for a programmable power supply such that with each successive change in voltage requirement for microprocessors the system designer will not have to completely re-engineer the power supply system. The voltage requirements of the microprocessor has been trending downwards over approximately the past 5 years, from 5 volts for the 386 and 486 microprocessors, to 3.3 volts for the Pentium, and now to down to 3.1 volts for the Pentium Pro.RTM.. There are indications that operating voltages for 1997 era microprocessors will be in the range of 2.5 volts.
Previous generations of dc--dc converter controllers have been designed with fixed output voltages or, in some cases, they have been adjustable by changing a set of external resistors. In the existing high volume production environment for personal computers, the central processing unit (CPU) board (also known as a "motherboard") has had to be redesigned each time the operating voltage has been changed by the microprocessor manufacturer. To address the problems caused by the changing voltage requirements, Intel.RTM., has programmed a voltage identification code (VID) into the Pentium Pro CPU which can be read by a motherboard that has the appropriate read capability. The motherboard, if it has the function built-in, then supplies the voltage identified by the VID to the CPU. This eliminates the requirement of the system designer to redesign the motherboard each time the CPU voltage changes because the CPU signals its own required voltage and the controller then automatically supplies the required voltage.
What is needed is a dc--dc converter controller designed with the ability to be programmed to address the changing power supply voltage needs for future lower voltage microprocessors. The dc--dc converter controller must be able to read the VID code programmed into the microprocessor and then supply the voltage called for by the microprocessor.